1. Field of the Invention
The present invention relates to an elastic shaft coupling apparatus which is capable of elastically transmitting a rotating force from an input-side member to an output-side member.
2. Description of the Related Art
In a conventional steering system, an elastic shaft coupling apparatus has a mechanism for prevention of tilting of an input shaft and an output shaft of the elastic shaft coupling apparatus is disclosed in Japanese Patent Application Publication No. 75405/1992. To summarize the structure of the just-mentioned elastic shaft coupling apparatus, as shown in FIG. 16, a pair of stopper plates s are respectively disposed on both sides of an elastic plate member e in such a manner as to face axial end sides of an input shaft c and an output shaft d.
The stopper plate s and the input shaft c on one side, and the stopper plate s and the output shaft d on the other side, are pin coupled together by means of bolts, thereby coupling the input shaft c and the output shaft d with the elastic plate member e clamped therebetween.
In this elastic shaft coupling structure, appropriate gaps are respectively provided between the respective stopper plates s and the end faces of the input shaft c and the output shaft d corresponding thereto. The input shaft c and the output shaft d are adapted to be rotatable relative to each other at an arbitrary rotating angle by virtue of deflection of the elastic plate member e. Further, a support shaft a projects from a center of either one of the stopper plates s. A receiving hole b for receiving the support shaft a is formed in an end face portion of the input shaft c or the output shaft d opposing that stopper plate s, and the support shaft a is inserted and disposed in the receiving hole b with an elastic material f disposed in the receiving hole b to surround the support shaft a.
If the above-described structure is adopted, drawbacks can occur such as that, due to an error in the assembly of the support shaft a of the stopper plate S and the input shaft c or the output shaft d, their axes become offset, and poor positional accuracy of the support shaft a of the stopper plate s results in misalignment between the axes of the support shaft a and the input shaft c or the output shaft d.
In such a case, in an inserting and coupling section formed by the support shaft a of the stopper plate s, which is fixed to either the input shaft c or the output shaft d, and the receiving hole b for receiving the support shaft a, the support shaft a of the stopper plate s is forcibly inserted in the receiving hole b due to the offset of the axes. As a result, the support shaft a of the stopper plate s and the receiving hole b are set in a mutually offset state, so that the support shaft a is set in a state of uneven contact with the elastic material f provided between the support shaft a and the inner peripheries of the receiving hole b.
Consequently, there occurs an increase in axial sliding resistance between the outer peripheral surface of the support shaft a of the stopper plate s and the elastic material f in the receiving hole b, which makes it impossible for the elastic plate member e to undergo smooth deflection in its axial direction. This also leads to the possibility of degrading the function of transmitting vibrations from the steering gear side to the steering shaft side while dampening the vibrations by means of the axial deflection of the elastic plate member e. Further, there is a possibility that variations in the amount of axial deflection of the elastic plate member e becomes large, causing variations in the spring constant in individual elastic shaft coupling apparatus and leading to instability in performance.
If a desired elastic shaft coupling apparatus is to be obtained which is capable of more substantially dampening the vibrations transmitted from the steering gear side to the steering shaft side, the above-described drawbacks necessitates the provision of a structure which increases the spring constant of the elastic plate member e (i.e., makes deflection difficult to occur) in the direction of relative rotation of the input shaft c and the output shaft d, and lowers the spring constant in the axial direction, thereby facilitating relative movement of the input shaft c and the output shaft d in the axial direction and stabilizing their movement in the axial direction.
In addition, to realize such a structure, it is conceivably necessary to enhance parts processing accuracy or assembling accuracy, or enlarge the clearance between the outer periphery of the support shaft a of the stopper plate S and the elastic material f accommodated in the receiving hole b, so as to expand an allowable range of movement. However, the former measure increases the product cost, and the latter measure has the possibility of making it impossible to sufficiently display the function for preventing the tilting of the input shaft c and the output shaft d in the elastic shaft coupling apparatus.